The present invention relates to stereoscopic projection systems and more particularly to a relatively distortion-free, "on axis" system which does not require the user to wear eyeglasses or utilize other means to separate the images. As used herein with respect to the present system, "on axis" means that the optical axes of both viewable images are optical axes of the spherical mirror and the centers of both images are located at the center of curvature of the spherical mirror.
Most conventional stereoscopic projection systems rely on various chromatic phenomena, polarization techniques, or like restrictions which are placed on the user. Use of eyewear containing such modifications limits the practicality of the system since it is difficult for the user's eyes to accommodate when attention must be devoted at a location in the room away from the stereoscopic image being viewed. Moreover, such eyewear is inconvenient to the user and contributes to the cost of the system.
Nevetheless, for many purposes, stereoscopic projection systems provide real advantages. Stereotactic neurosurgery could be enhanced, for example, if computer assisted X-ray tomagraphy images or nuclear magnetic resonance images could be processed in a computer and a composite of the brain projected as a stereo image. Relating this information on the location of brain tumors to the patient during surgery could be materially advanced by such a stereoscopic projection system. In fact, a non-distorted stereoscopic projection system in the operating room would be of even further benefit. Of course, other uses of a stereoscopic projection system outside of the medical field also can be readily envisioned. For example, in the aerodynamic design of surfaces (automobiles or aircraft) stereoscopic projection of the object being designed would be of benefit to the designer.
Prior proposals aimed at improving stereoscopic projection systems include U.S. Pats. Nos. 4,322,743 and 4,535,354. These systems, however, are not on axis and, therefore, exhibit unacceptable distortion patterns. Other proposals include U.S. Pats. Nos. 2,783,406 and 3,046,330. Despite these proposals, improved systems still are desired in this field.